The production of ceramic products or ceramic prostheses is very well known. Thus, for example, it is known to make use of die casting employing a tool which has a porous tool part through whose pores solvent, which has been released, is conducted away during the casting process. When producing dental bridges, for example, it is already known to use models of jawbone impressions and dental bridge shapes for producing dental bridge shells, which are to be coated with additional material for aesthetic shaping. It is also known to produce tools and tool parts to which the shape of the product or prosthesis can be transferred using a copying technique, after which the tool or tool part is used for spark machining a workpiece to form the product or prosthesis.
It is also well known to produce different types of wet compositions containing solvents and plaster and to use these in connection with making ceramic products in the form of coffee pots, lavatory seats, exhaust ports for internal combustion engines, etc. In this context, it is known to propose injection molding compositions which include ceramic powder or metallic or alloy powder which can be mixed into the melt of binding agent in the form of wax, polymers, etc. In connection with this, well-known technology proposes the use of dry crushing processes, dispersing agents, etc.
The body/product/prosthesis which is referred to above and which is produced using the present invention must be sinterable. The sintering confers the desired hardness on the body during the course of a certain degree of shrinkage. Such sintering is well known and is not part of the subject-matter of the present invention.
In connection with production of the product, there is a need for a technically simple tool for producing one or a few products, for example when making dental products, manufacturing prototypes, making products in small series, etc. In this context, the tool must have a technical construction, which permits economic use. The sole product, or the few products, must themselves carry the tool costs, which, in the case of dental bridge production, for example, implies a tool cost of only 20-30 SEK/product, calculated at present-day prices. The use of present-day technology and the manufacture of tool parts in, for example, high speed steel and the like results in a cost which is many times greater and which makes it impossible to produce the tools as disposable tools. This is one of the problems the invention is intended to solve.
In, for example, the production of dental products having individual and often complicated shapes, for example dental bridge shells, there is need to obtain a sinterable body/dental bridge, while retaining the high demands for fit which are placed on this body/dental bridge, by means of a single treatment step (molding). For example, it is difficult, when casting ceramic bodies, to prevent these bodies from buckling, which results in poor fitting shape. In accordance with the present invention, these problems are solved by special tool construction, tool production and a specially indicated injection molding composition.
Especially in the production of dental bridges, there is a general requirement for simplified methods for producing individually shaped products/bodies with a high degree of precision. The invention also provides solutions to this problem and makes it possible to create, in one and the same tool assembly, the underside and external contours of a body/dental bridge, which can extend between two or more teeth/attachment points in the dentine. In doing this, it is possible to avoid previous problems involved in creating bodies in several manufacturing steps, in which the external shape is transferred via a copying function is and the internal shape is produced by means of spark machining using a tool(s) to which the internal shape has previously been transferred by means of copying.
In connection with the injection molding of a product having a complicated shape, there is a need for heat to be conducted away in an efficient manner and for preventing distortion of the result by air cushion(s) which is/are trapped in the molding space. These problems, too, are solved by the invention, which proposes a specific heat-removal function using a heat conducting metal or alloy particles of specific quantity which are mixed into a tool part and which ensure that heat is conducted away in an appropriate manner. Thus, a well-balanced porosity in the tool part guarantees that air is removed in an appropriate manner from the molding space during the molding of the product. A porosity, which is too low, does not provide sufficient removal of air, and a porosity which is too high, with pore channels which are too large, results in the injection molding composition flowing out into the tool part.
When producing a tool part as described above, a wet composition is used whose solvent (water) is driven off by drying under ambient conditions or at an elevated temperature.
The demand placed on the material in the tool part, which is produced using the wet composition, is that it exhibits the properties, which are required as regards the injection molding and other aspects of the production. Thus, for example, the composition must be easy to shape or pour and, in the solidified state, exhibit shape-stability properties within given areas. It must be possible for the chemical reaction to take place at room temperature and it must be possible to regulate the porosity by means of pressure and temperature. The invention also solves these problems and recommends, as an example, that the modulus of elasticity should be&gt;1 GPa in the solidified material.
There is a need, in this connection, to obtain a coherent, sinterable body as the result of the injection molding. In addition, it must be easy to separate the body from the tool part, i.e. the material in the body must exhibit a certain flexibility so that the injection-molded body does not break when being separated from the tool part or tool parts. This places demands on the make-up of the injection molding composition, which, in addition, must be such that confluence or chemical reaction with the tool part produced from the wet composition does not take place. The invention also solves this problem.
In the production of the injection molding composition and the powder for this composition, it is essential that the powder agglomerate can be broken up and that preparation of the powder takes place in such a way that optimal homogeneity of the composition, without contamination, can be achieved using a limited number of process steps. It must be possible to hydrophobicize the powder surfaces efficiently by removing the excess of absorbed water. The dry matter content of the powder before it is mixed into the polymer melt and/or wax melt must be high, and it is advantageous if the energy consumption can be held down during the course of the admixing. The invention also solves these problems and proposes an effective preparation process prior to the admixture with the wax and/or the polymer.